The effects of a number of dietary variables on ruminal production of vitamin B12 and B12 analogues have already been quantitatively assessed. The degree to which analogues are absorbed, their identification in serum, urine and liver, and their possible involvement in bovine ketosis are items now to be investigated in this project. Absorption of Factor B will be estimated in sheep using the Co57- labelled compound administered at the duodenal level. Extracts of serum, urine and liver, including samples from normal and spontaneously ketotic cows will be subjected to electrophoresis and subsequent assay and compared with reference standards to identify and analogues present. The effects of Factor B, administered by intramuscular injection, on propionate metabolism will be studied in sheep and cattle.